Understanding of the functioning of the human brain would clearly benefit from physiological techniques able to provide dynamic maps of activity. Current electrophysiological and hemodynamic methods provide data with either good spatial or temporal resolution, but not both. Our preliminary studies indicate that non-invasive optical methods can provide a unique combination of spatial and temporal resolution that could be used to derive dynamic maps of brain activity. In addition, these techniques are compatible with other methods. However, our understanding of non-invasive optical methods is still incomplete. The specific purposes of the present project are: (a) to extend the preliminary findings about the sensitivity and spatial and temporal resolution of optical methods, (b) to provide initial data about the basic mechanisms underlying the optical signals, (c) to assess the ability of optical methods to provide depth information, and (d) to elucidate further the relationship between optical and electrical measures. The project will involve direct comparison of electrophysiological and optical data simultaneously recorded from the heads of normal human subjects with comparable spatial and temporal sampling. Structural, and in some cases functional, magnetic resonance data will also be acquired from the same subjects. The desired outcome is the development of tools for generating detailed spatio- temporal maps of brain activity during sensory, motor, and cognitive tasks. Possible future extensions include the application of the combined optical-electrophysiological approach to the study of the neurophysiology of cognition and neurological and psychiatric syndromes.